The Next Generation Network (“NGN”) architecture is an increasingly developing packet-based communications network architecture that is capable of providing various types of telecommunications services, including voice, video, and other data. The IP Multimedia Subsystem (“IMS”) is a NGN architecture originally defined by the 3rd Generation Partnership Project (“3GPP”). IMS can enable service providers to deploy new telecommunications services, simplify the network architecture by enabling Internet Protocol (“IP”) and Session Initiation Protocol (“SIP”) as a basis for communication, and facilitate fixed-mobile convergence.
NGNs are typically deployed with geographical redundancy in order to withstand the effects of site failures. Site failures may be caused by a power failure, a natural disaster, a cut cable, a damaged router, and various other network-related issues. In a typical geographical redundant deployment, subscriber information and other data stored in a critical subscriber database, such as a Home Subscriber Server (HSS), at a given site may be mirrored in a subscriber database at a remote site. In this way, data that cannot be retrieved due to the failure of one site can be recovered through the mirrored remote site.
The effectiveness of geographical redundancy may depend on the ability for the mirrored subscriber database to maintain the most current and correct data from the original subscriber database. Data coherence between the original subscriber database and the mirrored subscriber database may be ensured through a data synchronization process in which data that is updated in the original subscriber database is also updated in the mirrored subscriber database. This can be achieved by comparing time stamps associated with the data written to the original subscriber database with the time stamps associated with the data written to the mirrored subscriber database in order to determine whether the data in the mirrored subscriber database is current. If the mirrored subscriber database contains outdated data according to its time stamp, then the outdated data is overwritten with the current data from the original subscriber database.
While geographical redundancy as outlined above is suitable to recover from many catastrophic disasters, geographic redundancy has been shown to suffer drawbacks when a site-level failure is caused by certain types of network problems. In particular, after a first site operating a first subscriber database is isolated from other sites due to a network problem, subscribers may re-register with a second site in order to access a second subscriber database. Problems can occur, however, because network elements at the first site may continue to operate and update the time stamps at the first subscriber database with incorrect data. Thus, after the network problem is fixed at the first site, the data synchronization process may cause the second subscriber database to be updated with the incorrect data from the first subscriber database if the incorrect data has a newer time stamp.